The present invention relates to a semiconductor device and, more particularly to a high power semiconductor device adapted for use, for example, in a thyristor chopper controller equipped in an electric vehicle.
In designing a high power semiconductor device, considerations must be made on pressing the semiconductor pellet, heat dissipation from the semiconductor pellet and electric connection, so as to meet the requirements that the heat produced by the current within the semiconductor pellet must be dissipated effectively, the semiconductor pellet must be protected from dielectric breakdown caused by the humidity or contamination with dusts, and the semiconductor device must be compact and of light weight.
Conventionally, semiconductor devices have been structured as disclosed typically in U.S. Pat. No. 3,886,586.
The semiconductor device shown in the abovementioned patent comprises upper and lower metal cover plates fixed on an iron ring, and a semiconductor pellet press-fitted to a metal plate located above the pellet with the periphery of the semiconductor pellet being surrounded by an insulation ring formed of such as aluminum oxide.
In the above-mentioned arrangement, the semiconductor pellet and metal cover plate, and the metal cover plate and metal plate form planar connections which are achieved by soldering. The upper and lower iron rings and the peripheral insulation ring are required to have air-tightness, and they are fitted by hard soldering.
Therefore, in spite of the fact that the structure is made up of relatively simple component parts, the fabricating process for the above-mentioned semiconductor device cannot be simplified. The foregoing structure is also disadvantageous from the viewpoint of maintenance of the semiconductor device. Moreover, soldering of components does not provide sufficient reliability for such uses that requires a high durability against vibration, as in electric automobiles.